There is conventionally known a topology in which a network is constructed by connecting between communication terminals (hereinafter, “communication nodes”) using FDDI (Fiber-Distributed Data Interface) (for example, Nonpatent literature 1). In the FDDI, generally, a network is constructed so that communication nodes are connected in a ring. The network using the FDDI is formed of a dual-loop structure having a first loop in which data is transmitted in a normal state, and a second loop which is configured so as to enable communication using a normal portion, when abnormality such as disconnection of a cable forming the first loop and failure in a communication node occurs, by performing loop-back so as to disconnect an abnormal portion from the network.
Further, the FDDI employs a token passing system that provides controls so that collisions of data transmitted between communication nodes connected to the network do not occur by using data for the right to transmit called a token. The token passing system is implemented in such a manner that a token is passed around the first loop, and a communication node wishing to transmit data takes the token, passes data instead that the communication node itself wishes to transmit, and releases the token again to the network when the transmission is finished, so that only one terminal can use the cable at a time.
Nonpatent literature 1: “Details of FDDI Technology-Construction of 100 Mbps LAN-” written by Karl F. Pieper, William J. Cronin Jr., and Wendy H. Michael, translated and supervised by Naoki Mizutame, first edition, published by Kyoritsu Shuppan Co., Aug. 30, 1993, p. 67 to 73.